Just some wild ideas: If they fly up from the ground, are they maybe concerned about not hitting a bar correctly and landing between the bars? Don't know anything about bantys, but can they see enough from the ground to see the landing site--or do they just see the edge of the poop board? They need enough horizontal space and visibility to fly up and down, not hit the poop board on the way, and to not feel trapped by other birds. Also, maybe they don't feel any more secure on the roosts than on the floor because the poop board is seems to jut out so far? The roost needs to "feel" safer than the other spaces in the coop. It just seems more like a half of n oven rack on a super wide poop board than an actual roost, up high where they would enjoy being. Maybe try just using boot trays under a single roost and dispense with the poop board?
Mine prefer WIDE roosts and did not start roosting until many, many months old. Given a choice today, they still prefer to huddle under Mr. Roo. Also, laying regularly in the boxes came over time for some. Some need time to learn their new roles.
Good luck with your next batch. I think a small coop may present its own challenges. Maybe look at some other interiors?